Method for testing condensation point of crude oil by coupon method

Abstract

The invention provides a method for testing the condensation point of crude oil through a coupon method, and belongs to the technical field of oil transportation and rheology. The hanging piece is hung in the oil sample to be measured through the tension meter, the tension borne by the hanging piece in the oil sample to be measured is measured in a slow cooling mode, and when no gel structure is formed in the oil sample to be measured, the tension borne by the hanging piece is basically unchanged; after a gelling structure in an oil sample to be measured is formed, a downward normal stress is generated on the hanging piece based on the volume shrinkage characteristic of crude oil, so that the tensile force of the tension meter is remarkably increased, the tensile force is directly displayed on the readings of the tension meter, the temperature at the moment is recorded, and then the readings of the subsequent three tension meters are recorded; errors caused by factors such as external force are avoided, so that the condensation point of the crude oil can be directly judged according to the reading of the tension meter. The method is simple and applicable to operation, objective in judgment mode and reliable in principle, and can accurately judge the temperature of the gelling structure generated in the cooling process of the crude oil, so that the condensation point of the crude oil is directly judged.

Description

Technical Field

[0001] The present invention relates to the technical fields of oil transportation and rheology, and particularly relates to a method for testing the pour point of crude oil by the hanging slice method. Background Art

[0002] Most of the crude oil produced in China belongs to paraffin-based crude oil, which has a high pour point, poor low-temperature fluidity, great exploitation difficulty, and high transportation energy consumption. At high temperatures, the fluidity of crude oil is good; below the wax precipitation point, the rheology will deteriorate significantly; when the wax precipitation amount reaches 2-3% of the crude oil, due to the cross-linking of wax crystal particles to form a network structure, the crude oil will gel, showing complex rheological properties such as yield stress and viscoelasticity, and ultimately losing fluidity, which poses a huge challenge to the transportation safety of crude oil. The pour point of crude oil is an important indicator for judging whether the crude oil can maintain fluidity during the cooling process, and has important guiding significance for formulating pipeline transportation processes and ensuring transportation safety.

[0003] However, the concept of the pour point of crude oil is conditional. At the same time, crude oil is extremely sensitive to conditions such as thermal history and shear history, which makes the determination of the pour point depend on specific test conditions. To standardize this process, domestic and foreign institutions have formulated a series of pour point test standards. The current SY / T 0541-2009 "Determination Method for Pour Point of Crude Oil" uses the fact that the liquid level of the crude oil in the pour point test tube does not move horizontally for 5 s as the basis for judging the pour point. However, in actual operation, the jitter when taking out the test tube may destroy the formation of the gel structure of the crude oil, and the judgment of the inclination angle and the fluidity of the crude oil often depends on subjective visual evaluation, with many influencing factors and lack of objectivity. In addition, some scholars use a rheometer to conduct dynamic cooling tests on crude oil and determine the gel point of the crude oil by the change of the viscoelastic modulus. Although this method has a certain scientific nature in theory, its requirements for test equipment are relatively high, which limits its application in the field.

[0004] Therefore, providing a method for testing the pour point of crude oil with simple operation and few error factors is crucial for the storage and transportation of crude oil and has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for testing the pour point of crude oil by the hanging slice method. The method provided by the present invention is simple and applicable in operation, the judgment method is objective, and the principle is reliable, and can accurately judge the temperature at which the gel structure is generated during the cooling process of the crude oil, so as to directly judge the pour point of the crude oil.

[0006] To achieve the above invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for testing the pour point of crude oil by the hanging slice method, including the following steps:

[0008] (1) Inject equal amounts of the oil sample to be tested into two freezing point test tubes respectively, obtaining two freezing point test tubes containing the oil sample to be tested;

[0009] (2) Insert the stopper with the freezing point thermometer into one of the freezing point test tubes containing the oil sample to be tested obtained in the step (1), obtaining a freezing point test tube with a freezing point thermometer;

[0010] (3) Put the other freezing point test tube containing the oil sample to be tested obtained in the step (1) and the freezing point test tube with the freezing point thermometer obtained in the step (2) into the freezing point test sleeve at the same time, and hang the hanging piece into the other freezing point test tube containing the oil sample to be tested obtained in the step (1), with the other end of the hanging piece connected to the tensiometer, obtaining the device to be tested; the hanging piece is a two-blade paddle hanging piece, a four-blade paddle hanging piece or a double flat plate hanging piece;

[0011] (4) Cool the two freezing point test tubes of the device to be tested in the step (3), use the freezing point test tube with the thermometer in the step (3) as a reference sample for reading the temperature, record the reading of the tensiometer every 0.5 - 1 °C. When the reading of the tensiometer suddenly increases, record the temperature at this time, and continue to record the readings of the tensiometer for three times. When the readings of the subsequent three tensiometers return to the equilibrium value before the increase, continue to record the readings of the tensiometer. When the readings of the subsequent three tensiometers are all greater than the tensile equilibrium value before the increase, the temperature recorded when the reading of the tensiometer suddenly increases is the freezing point of the oil sample to be tested.

[0012] Preferably, the freezing point test tubes in the step (1) are dry and clean freezing point test tubes.

[0013] Preferably, before injecting equal amounts of the oil sample to be tested into the two freezing point test tubes in the step (1), preheat the two freezing point test tubes and the oil sample to be tested respectively.

[0014] Preferably, the preheating temperature is 35 - 70 °C, and the preheating time is 20 - 40 min.

[0015] Preferably, the injection amount of the oil sample to be tested in the step (1) is up to the 50 ± 3 mm circular scale line of the freezing point test tube.

[0016] Preferably, the freezing point thermometer in the freezing point test tube with the freezing point thermometer in the step (2) is perpendicular to the center of the freezing point test tube; the distance between the mercury bulb of the freezing point thermometer and the bottom of the freezing point test tube is 20 ± 2 mm.

[0017] Preferably, the freezing point test sleeve in the step (3) is directly below the tensiometer.

[0018] Preferably, in the step (3), the width of the blade of the two-blade paddle-shaped hanging piece is 10-13 mm, the height of the blade of the two-blade paddle-shaped hanging piece is 10-13 mm, and the thickness of the blade of the two-blade paddle-shaped hanging piece is 0.5-1 mm; the width of the blade of the four-blade paddle-shaped hanging piece is 10-13 mm, the height of the blade of the four-blade paddle-shaped hanging piece is 10-13 mm, and the thickness of the blade of the four-blade paddle-shaped hanging piece is 0.5-1 mm; the diameter of the flat plate of the double-flat-plate hanging piece is 10-13 mm, the thickness of the flat plate of the double-flat-plate hanging piece is 0.5-1 mm, and the distance between the two blades of the double-flat-plate hanging piece is 6-10 mm; the diameters of the support columns of the two-blade paddle-shaped hanging piece, the four-blade paddle-shaped hanging piece and the double-flat-plate hanging piece are independently 2.5-3 mm, and the heights are independently 1.5-2 mm.

[0019] Preferably, in the step (3), the hanging piece is connected to a tensiometer by a thin wire, the uppermost end of the hanging piece is flush with the annular scale line of the freezing point test tube, and the hanging piece does not contact the wall surface of the freezing point test tube.

[0020] Preferably, in the step (3), the freezing point test sleeve is vertically installed in the temperature control device, and the temperature control device contains a coolant; the depth of immersion of the freezing point test sleeve in the coolant is ≥100 mm; the temperature difference between the temperature of the oil sample to be tested and the coolant is 10-25 °C; the cooling rate of the temperature control device is 0.5-1 °C / min.

[0021] The present invention provides a method for testing the pour point of crude oil by the hanging piece method, which includes the following steps: (1) Inject equal amounts of the oil sample to be tested into two pour point test tubes to obtain two pour point test tubes containing the oil sample to be tested; (2) Insert a stopper with a pour point thermometer into one of the pour point test tubes containing the oil sample to be tested obtained in step (1) to obtain a pour point test tube with a pour point thermometer; (3) Put the other pour point test tube containing the oil sample to be tested obtained in step (1) and the pour point test tube with a pour point thermometer obtained in step (2) into the pour point test sleeve at the same time, and hang the hanging piece into the other pour point test tube containing the oil sample to be tested obtained in step (1), and the other end of the hanging piece is connected to a tensiometer to obtain the device to be tested; the hanging piece is a two-blade paddle-shaped hanging piece, a four-blade paddle-shaped hanging piece or a double-plate hanging piece; (4) Cool the two pour point test tubes of the device to be tested in step (3), and use the pour point test tube with a thermometer in step (3) as a reference sample to read the temperature. Record the reading of the tensiometer every 0.5 - 1 °C. When the reading of the tensiometer suddenly increases, record the temperature at this time, and continue to record the readings of the tensiometer three times. When the readings of the subsequent three tensiometers return to the equilibrium value before the increase, continue to record the readings of the tensiometer. When the readings of the subsequent three tensiometers are all greater than the tensile equilibrium value before the increase, the temperature recorded when the reading of the tensiometer suddenly increases is the pour point of the oil sample to be tested. In the present invention, the hanging piece is suspended in the oil sample to be tested through a tensiometer, and the tensile force received by the hanging piece in the oil sample to be tested is measured by slowly lowering the temperature. When there is no gel structure formed in the oil sample to be tested, the tensile force received by the hanging piece remains basically unchanged; after the gel structure is formed in the oil sample to be tested, based on the volume shrinkage characteristic of the crude oil, a normal stress acting downward will be generated on the hanging piece, causing the tensile force of the tensiometer to increase significantly, which will be directly shown in the reading of the tensiometer. Record the temperature at this time, and then record the readings of the subsequent three tensiometers, avoiding errors caused by external forces and other factors. Therefore, the pour point of the crude oil can be directly judged according to the reading of the tensiometer. The method provided by the present invention is simple and applicable in operation, the judgment method is objective and the principle is reliable, and it can accurately judge the temperature at which the gel structure is formed during the cooling process of the crude oil, so as to directly judge the pour point of the crude oil. The results of the examples show that when measuring the pour points of Nanyang crude oil, Changqing crude oil, Linpan crude oil and simulated wax oil by the method provided by the present invention, only the value of the tensiometer needs to be read regularly, and there is no need to repeatedly observe the pour point test tube, and the obtained results have good stability and low error value (±0.5 °C). BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The main structural view of the two-blade paddle-shaped hanging piece;

[0023] Figure 2 The top view of the two-blade paddle-shaped hanging piece;

[0024] Figure 3 The main structural view of the four-blade paddle-shaped hanging piece;

[0025] Figure 4 It is a top view of the structure of the 4 - blade paddle - type hanging piece;

[0026] Figure 5 It is a front view of the structure of the double - flat - plate hanging piece;

[0027] Figure 6 It is a top view of the structure of the double - flat - plate hanging piece;

[0028] Figure 7 It is a schematic structural diagram formed when testing the pour point of crude oil by the hanging - piece method provided by the present invention;

[0029] Figure 8 It is the relationship curve of the pulling force and temperature of the pull - meter in Examples 1 - 3. Detailed implementation manners

[0030] The present invention provides a method for testing the pour point of crude oil by the hanging - piece method, including the following steps:

[0031] (1) Inject equal amounts of the oil sample to be tested into two pour - point test tubes respectively to obtain two pour - point test tubes containing the oil sample to be tested;

[0032] (2) Insert the stopper with a pour - point thermometer into one of the pour - point test tubes containing the oil sample to be tested obtained in step (1) to obtain a pour - point test tube with a pour - point thermometer;

[0033] (3) Put the other pour - point test tube containing the oil sample to be tested obtained in step (1) and the pour - point test tube with a pour - point thermometer obtained in step (2) into the pour - point test sleeve at the same time, and hang the hanging piece into the other pour - point test tube containing the oil sample to be tested obtained in step (1), and connect the other end of the hanging piece to the pull - meter to obtain the device to be tested; the hanging piece is a 2 - blade paddle - type hanging piece, a 4 - blade paddle - type hanging piece or a double - flat - plate hanging piece;

[0034] (4) Cool the two pour - point test tubes of the device to be tested in step (3), use the pour - point test tube with a thermometer in step (3) as a reference sample for reading the temperature, record the reading of the pull - meter every 0.5 - 1 °C. When the reading of the pull - meter suddenly increases, record the temperature at this time, and continue to record the readings of the pull - meter for three times. When the readings of the subsequent three pull - meters return to the equilibrium value before the increase, continue to record the readings of the pull - meter. When the readings of the subsequent three pull - meters are all greater than the pull - force equilibrium value before the increase, the temperature recorded when the reading of the pull - meter suddenly increases is the pour point of the oil sample to be tested.

[0035] The present invention injects equal amounts of the oil sample to be tested into two pour - point test tubes respectively to obtain two pour - point test tubes containing the oil sample to be tested.

[0036] In the present invention, the sources of the oil samples to be tested are preferably the same. The present invention has no special limitation on the specific sources of the oil samples to be tested. Oil samples from any region can be used, as long as the oil samples to be tested in the two freezing point test tubes are exactly the same.

[0037] In the present invention, the freezing point test tubes preferably comply with the provisions of SY / T 0541-2009 "Method for Determination of Pour Point of Crude Oil". In the present invention, the freezing point test tubes are preferably dry and clean freezing point test tubes. In the present invention, when the freezing point test tubes do not meet the above requirements, it is preferred to clean and dry the freezing point test tubes. The present invention has no special limitation on the specific operations of the cleaning and drying, as long as the freezing point test tubes can be ensured to be dry and clean. By using dry and clean freezing point test tubes in the present invention, the influence of impurities such as moisture and dust on the test results can be avoided, thereby reducing the influence of external factors.

[0038] In the present invention, it is preferred to preheat the two freezing point test tubes and the oil samples to be tested respectively before injecting equal amounts of the oil samples to be tested into the two freezing point test tubes. The present invention has no special limitation on the temperature, time and method of the preheating, as long as the preheating temperatures of the freezing point test tubes and the oil samples to be tested are the same. As an implementation manner of the present invention, the temperature of the preheating can be 35-70 °C, and can also be 35 °C, 38 °C, 40 °C, 42 °C, 45 °C, 48 °C, 50 °C, 52 °C, 55 °C, 60 °C, 65 °C or 70 °C; the time of the preheating can be 20-40 min, and can also be 20 min, 25 min, 30 min, 35 min or 40 min; the method of the preheating can be a warm water bath; the oil samples to be tested can be first placed in a ground glass bottle and then preheated; the ground glass bottle preferably complies with the provisions of SY / T 0541-2009 "Method for Determination of Pour Point of Crude Oil". By preheating the freezing point test tubes in the present invention, it can be avoided that the temperature of the oil samples to be tested drops rapidly when the oil samples to be tested are added to the freezing point test tubes, and further, the problem that the oil samples to be tested gel before the test and affect the test results can be avoided.

[0039] In the present invention, the injection amount of the oil samples to be tested is preferably up to the annular marking line at 50±3 mm of the freezing point test tube. By controlling the injection amount of the oil samples to be tested in the present invention, it is convenient for the subsequent introduction of the freezing point thermometer and the hanging piece.

[0040] After obtaining two freezing point test tubes containing the oil samples to be tested, the present invention inserts the stopper with the freezing point thermometer into the one freezing point test tube containing the oil samples to be tested to obtain a freezing point test tube with a freezing point thermometer.

[0041] In the present invention, the freezing point thermometer is preferably a mercury thermometer; the mercury thermometer preferably complies with the provisions of SY / T0541-2009 "Method for Determination of Pour Point of Crude Oil".

[0042] In the present invention, the freezing point thermometer in the freezing point test tube with a freezing point thermometer is preferably perpendicular to the center of the freezing point test tube; the distance between the mercury bulb of the freezing point thermometer and the bottom of the freezing point test tube is preferably 20 ± 2 mm. In the present invention, when the position of the freezing point thermometer does not meet the above requirements, it is preferred to adjust the position of the freezing point thermometer before inserting the stopper with the freezing point thermometer; the adjustment method is preferably to take an identical freezing point test tube, insert the stopper with the freezing point thermometer into the freezing point test tube, then adjust the position of the freezing point thermometer to make it meet the above requirements and keep it unchanged, and then take out the stopper with the freezing point thermometer for standby. By controlling the position of the freezing point thermometer, the present invention is conducive to the freezing point thermometer more accurately measuring the freezing point of the oil sample to be tested and reducing errors.

[0043] After obtaining the freezing point test tube with a freezing point thermometer, the present invention simultaneously places the other freezing point test tube containing the oil sample to be tested and the freezing point test tube with a freezing point thermometer into the freezing point test sleeve, and suspends the hanging piece into the other freezing point test tube containing the oil sample to be tested. The other end of the hanging piece is connected to a tensiometer to obtain the device to be tested.

[0044] In the present invention, the freezing point test sleeve preferably complies with the provisions of SY / T 0541-2009 "Method for Determining the Freezing Point of Crude Oil". In the present invention, the freezing point test sleeve is preferably directly below the tensiometer. In the present invention, the range of the tensiometer is preferably ≥2 N; the graduation value of the tensiometer is preferably 10 -4 N; the accuracy of the tensiometer is preferably ±0.5%. Through the above operations, the present invention can suspend the hanging piece in the freezing point test tube without contacting the freezing point test tube, thereby reducing the interference of external forces and further improving the test accuracy.

[0045] In the present invention, the hanging piece is a two-blade paddle-type hanging piece, a four-blade paddle-type hanging piece or a double-plate hanging piece. In the present invention, the material of the hanging piece is preferably stainless steel; the surface roughness Ra of the hanging piece is preferably 5-6 μm. In the present invention, the front view of the structure of the two-blade paddle-type hanging piece is as Figure 1 shown; the top view of the structure of the two-blade paddle-type hanging piece is as Figure 2 shown; the front view of the structure of the four-blade paddle-type hanging piece is as Figure 3 shown; the top view of the structure of the four-blade paddle-type hanging piece is as Figure 4 shown; the front view of the structure of the double-plate hanging piece is as Figure 5 shown; the top view of the structure of the double-plate hanging piece is as Figure 6As shown. The present invention does not have special limitations on the specific dimensions of the hanging piece, and it can be determined according to the common technical knowledge of those skilled in the art. As an embodiment of the present invention, the width of the hanging piece of the two-blade paddle-shaped hanging piece can be 10-13 mm, and can also be 12 mm; the height of the paddle blade of the two-blade paddle-shaped hanging piece can be 10-13 mm, and can also be 12 mm; the thickness of the paddle blade of the two-blade paddle-shaped hanging piece can be 0.5-1 mm, and can also be 0.8 mm; the width of the hanging piece of the four-blade paddle-shaped hanging piece can be 10-13 mm, and can also be 12 mm; the height of the paddle blade of the four-blade paddle-shaped hanging piece can be 10-13 mm, and can also be 12 mm; the thickness of the paddle blade of the four-blade paddle-shaped hanging piece can be 0.5-1 mm, and can also be 0.8 mm; the diameter of the flat plate of the double-flat-plate hanging piece can be 10-13 mm, and can also be 12 mm; the thickness of the flat plate of the double-flat-plate hanging piece can be 0.5-1 mm, and can also be 0.8 mm; the distance between the two paddle blades of the double-flat-plate hanging piece can be 6-10 mm, and can also be 8 mm; the diameter of the support column of the two-blade paddle-shaped hanging piece, four-blade paddle-shaped hanging piece and double-flat-plate hanging piece can independently be 2.5-3 mm, and can also be 2.8 mm; the height of the two-blade paddle-shaped hanging piece, four-blade paddle-shaped hanging piece and double-flat-plate hanging piece can independently be 1.5-2 mm, and can also be 1.8 mm. The present invention does not have special limitations on the specific source and preparation method of the hanging piece. Commercially available hanging pieces well-known to those skilled in the art can be used or prepared by known methods, as long as the structure and dimensions of the hanging piece meet the requirements. By using the hanging piece with the above structure for tensile force calculation in the present invention, the contact area between the hanging piece and the oil sample to be measured is larger, so that the change in the tensile force received is more obvious, and further reduces the influence of errors.

[0046] In the present invention, the hanging piece is preferably connected to a tensiometer through a thin wire; the uppermost end of the hanging piece is preferably flush with the annular scale line of the pour point test tube; the hanging piece preferably does not contact the wall surface of the pour point test tube. The present invention does not have special limitations on the material and dimensions of the thin wire, and commercially available thin wires well-known to those skilled in the art can be used. Through the above settings in the present invention, errors caused by external forces such as friction can be reduced, thereby improving the detection accuracy.

[0047] In the present invention, the pour point test sleeve is preferably vertically installed in the temperature control device; the temperature control device preferably contains a coolant; the depth of immersion of the pour point test sleeve in the coolant is preferably ≥100 mm; the temperature difference between the oil sample to be tested and the coolant is preferably 10 - 25 °C; the cooling rate of the temperature control device is preferably 0.5 - 1 °C / min, more preferably 0.75 °C / min. In the present invention, the temperature control device preferably complies with the provisions of SY / T 0541-2009 "Method for Determination of Pour Point of Crude Oil". In the present invention, by immersing the pour point test sleeve in the coolant, and using the temperature difference between the coolant and the oil sample to be tested and the cooling rate of the temperature control device to slowly decrease the temperature of the oil sample to be tested, so that the temperature of the oil sample to be tested slowly reaches the pour point, and then accurately obtains the temperature when the tensile force changes; by controlling the depth of immersion of the pour point test sleeve in the coolant, the overall temperature of the oil sample to be tested can be synchronously decreased, avoiding the problem that the error becomes larger due to uneven internal temperature distribution of the oil sample to be tested.

[0048] The present invention has no special limitation on the time for putting the other pour point test tube containing the oil sample to be tested and the pour point test tube with a pour point thermometer into the pour point test sleeve. In order to avoid a temperature difference between the two pour point test tubes in the air, they should be put in smoothly and quickly to avoid shaking of the oil sample to be tested. As an embodiment of the present invention, the time difference for putting the other pour point test tube containing the oil sample to be tested and the pour point test tube with a pour point thermometer into the pour point test sleeve is preferably <30 s. By controlling the time difference for putting the two pour point test tubes into the pour point test sleeve, the present invention can avoid generating a temperature difference between the two during the transfer process and affecting the test result.

[0049] The present invention has no special limitation on the hanging rate for hanging the coupon into the pour point test tube, as long as it can avoid the surface of the oil sample to be tested in the pour point test tube from fluctuating.

[0050] After obtaining the device to be tested, the present invention cools the two pour point test tubes of the device to be tested, uses the pour point test tube with a thermometer as a reference sample for reading the temperature, records the reading of the tensiometer every 0.5 - 1 °C. When the reading of the tensiometer suddenly increases, record the temperature at this time, and continue to record the readings of the tensiometer for three times. When the subsequent three readings of the tensiometer return to the equilibrium value before the increase, continue to record the readings of the tensiometer. When the subsequent three readings of the tensiometer are all greater than the tensile force equilibrium value before the increase, the temperature recorded when the reading of the tensiometer suddenly increases is the pour point of the oil sample to be tested.

[0051] In the present invention, the cooling method is preferably to use a temperature control device for cooling. In the present invention, the temperature control device is preferably the aforementioned temperature control device, which will not be elaborated here.

[0052] The schematic diagram of the structure formed during the determination of the pour point of crude oil by the hanging slice method provided by the present invention is as follows Figure 7 as shown. It can be seen from Figure 7 that in two pour point test tubes containing equal amounts of the oil sample to be tested, one pour point test tube fixes the pour point thermometer through a stopper. The pour point thermometer is located at the central position of the pour point test tube, and there is a certain distance between the mercury bulb of the pour point test tube and the bottom of the pour point test tube. While in the other pour point test tube, a hanging slice is suspended inside. The hanging slice is connected to a tensiometer through a thin wire, and the position of the hanging slice in the pour point test tube is adjusted by a height adjustment bracket; at the same time, the two pour point test tubes are installed in a pour point test sleeve, and the pour point test sleeve is connected to a temperature control device. The temperature control device controls the temperature of the oil sample to be tested by controlling the temperature of the water bath, and determines the normal stress generated by the oil sample to be tested on the hanging slice through the tensiometer. Thus, the pour point of the oil sample to be tested is determined by the change in the tension of the tensiometer when the temperature of the oil sample to be tested reaches the pour point.

[0053] In the present invention, the hanging slice is suspended in the oil sample to be tested through a tensiometer, and the tension received by the hanging slice in the oil sample to be tested is measured by slowly lowering the temperature. When no gel structure is formed in the oil sample to be tested, the tension received by the hanging slice remains basically unchanged; after the gel structure is formed in the oil sample to be tested, based on the volume shrinkage characteristic of the crude oil, a downward normal stress will be generated on the hanging slice, causing the tension of the tensiometer to increase significantly, and this will be directly shown in the reading of the tensiometer. Record the temperature at this time, and then record the readings of the subsequent three tensiometers to avoid errors caused by external forces and other factors. Therefore, the pour point of the crude oil can be directly judged according to the reading of the tensiometer. The method provided by the present invention is simple and applicable in operation, the judgment method is objective, the principle is reliable, and it can accurately judge the temperature at which the gel structure is formed during the cooling process of the crude oil, so as to directly judge the pour point of the crude oil.

[0054] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0055] The instruments used in the embodiments are as follows:

[0056] The pour point test tube complies with the provisions of SY / T 0541-2009 "Method for Determination of Pour Point of Crude Oil";

[0057] The ground glass bottle complies with the provisions of SY / T 0541-2009 "Method for Determination of Pour Point of Crude Oil";

[0058] The pour point thermometer is a mercury thermometer and complies with the provisions of SY / T 0541-2009 "Method for Determination of Pour Point of Crude Oil";

[0059] The pour point test casing complies with the provisions of SY / T 0541-2009 "Determination Method for Pour Point of Crude Oil";

[0060] The temperature control device complies with the provisions of SY / T 0541-2009 "Determination Method for Pour Point of Crude Oil";

[0061] The range of the tensiometer ≥ 2 N, the graduation value of the tensiometer is 10 -4 N, and the accuracy of the tensiometer is ±0.5%.

[0062] Example 1

[0063] A method for testing the pour point of crude oil by the coupon method, which is the following steps:

[0064] (1) First place the oil sample to be tested in a ground glass bottle, and then preheat it. The preheating temperature is 60 °C, the time is 30 min, and the preheating method is a warm water bath. Then inject the preheated oil sample to be tested into two preheated, dried and clean pour point test tubes respectively until the annular marking line of 50 ± 3 mm of the pour point test tube is reached, obtaining two pour point test tubes containing the oil sample to be tested; the oil sample to be tested is Nanyang crude oil;

[0065] (2) Insert the stopper with the pour point thermometer into one of the pour point test tubes containing the oil sample to be tested obtained in the step (1). The pour point thermometer is perpendicular to the center of the pour point test tube, and the distance between the mercury bulb of the pour point thermometer and the bottom of the pour point test tube is 20 mm, obtaining a pour point test tube with a pour point thermometer;

[0066] (3) Put the other pour point test tube containing the oil sample to be tested obtained in the step (1) and the pour point test tube with the pour point thermometer obtained in the step (2) into the pour point test casing at the same time, and hang the coupon into the other pour point test tube containing the oil sample to be tested obtained in the step (1). The pour point test casing is directly below the tensiometer. The other end of the coupon is connected to the tensiometer by a thin wire. The uppermost end of the coupon is flush with the annular marking line of the pour point test tube, and the coupon does not contact the wall of the pour point test tube, obtaining the device to be tested; the coupon is a 2-blade paddle coupon (denoted as coupon 1); the width of the 2-blade paddle coupon is 12 mm, the height of the paddle blade is 12 mm, and the thickness of the paddle blade is 0.8 mm; the diameter of the support column of the 2-blade paddle coupon is 2.8 mm and the height is 1.8 mm; the pour point test casing is vertically installed in the temperature control device. The temperature control device contains coolant. The depth of the pour point test casing immersed in the coolant is 100 mm. The temperature difference between the oil sample to be tested and the coolant is 15 °C, and the cooling rate of the temperature control device is 0.75 °C / min;

[0067] (4) Cool the two freezing point test tubes of the device to be tested in step (3). Use the freezing point test tube with a thermometer in step (3) as a reference sample to read the temperature. Record the reading of the tensiometer every 0.5 °C. When the reading of the tensiometer suddenly increases, record the temperature at this time, and continue to record the readings of the tensiometer for three times. When the readings of the subsequent three tensiometers return to the equilibrium value before the increase, continue to record the readings of the tensiometer. When the readings of the subsequent three tensiometers are all greater than the tensile equilibrium value before the increase, the temperature recorded when the reading of the tensiometer suddenly increases is the freezing point of the oil sample to be tested.

[0068] Example 2

[0069] A method for testing the freezing point of crude oil by the coupon method, comprising the following steps:

[0070] (1) First place the oil sample to be tested in a ground glass bottle, and then preheat it. The preheating temperature is 60 °C, the time is 30 min, and the preheating method is a warm water bath. Then inject the preheated oil sample to be tested into two preheated, dry and clean freezing point test tubes respectively up to the annular scale line at 50 ± 3 mm of the freezing point test tube, obtaining two freezing point test tubes containing the oil sample to be tested; the oil sample to be tested is Nanyang crude oil.

[0071] (2) Insert a stopper with a freezing point thermometer into one of the freezing point test tubes containing the oil sample to be tested obtained in step (1). The freezing point thermometer is perpendicular to the center of the freezing point test tube, and the distance between the mercury bulb of the freezing point thermometer and the bottom of the freezing point test tube is 20 mm, obtaining a freezing point test tube with a freezing point thermometer.

[0072] (3) Place the other freezing point test tube containing the oil sample to be tested obtained in step (1) and the freezing point test tube with a freezing point thermometer obtained in step (2) into the freezing point test sleeve at the same time, and hang the coupon into the other freezing point test tube containing the oil sample to be tested obtained in step (1). The freezing point test sleeve is directly below the tensiometer. The other end of the coupon is connected to the tensiometer by a thin wire. The top end of the coupon is flush with the annular scale line of the freezing point test tube, and the coupon does not touch the wall of the freezing point test tube, obtaining the device to be tested; the coupon is a 4-blade paddle coupon (denoted as coupon 2); the width of the 4-blade paddle coupon is 12 mm, the height of the paddle blade is 12 mm, and the thickness of the paddle blade is 0.8 mm; the diameter of the support column of the 4-blade paddle coupon is 2.8 mm, and the height is 1.8 mm; the freezing point test sleeve is vertically installed in the temperature control device. The temperature control device contains a coolant. The depth of the freezing point test sleeve immersed in the coolant is 100 mm. The temperature difference between the oil sample to be tested and the coolant is 15 °C, and the cooling rate of the temperature control device is 0.75 °C / min.

[0073] (4) Cool the two freezing point test tubes of the device to be tested in step (3). Use the freezing point test tube with a thermometer in step (3) as a reference sample for reading the temperature. Record the reading of the tensiometer every 0.5 °C. When the reading of the tensiometer suddenly increases, record the temperature at this time, and continue to record the readings of the tensiometer for three times. When the readings of the subsequent three tensiometers return to the equilibrium value before the increase, continue to record the readings of the tensiometer. When the readings of the subsequent three tensiometers are all greater than the tensile equilibrium value before the increase, the temperature recorded when the reading of the tensiometer suddenly increases is the freezing point of the oil sample to be tested.

[0074] Example 3

[0075] A method for testing the freezing point of crude oil by the coupon method, comprising the following steps:

[0076] (1) First place the oil sample to be tested in a ground glass bottle, and then preheat it. The preheating temperature is 60 °C, the time is 30 min, and the preheating method is a warm water bath. Then inject the preheated oil sample to be tested into two preheated, dried and clean freezing point test tubes respectively up to the 50 ± 3 mm circular scale line of the freezing point test tube, obtaining two freezing point test tubes containing the oil sample to be tested; the oil sample to be tested is Nanyang crude oil.

[0077] (2) Insert a stopper with a freezing point thermometer into one of the freezing point test tubes containing the oil sample to be tested obtained in step (1). The freezing point thermometer is perpendicular to the center of the freezing point test tube, and the distance between the mercury bulb of the freezing point thermometer and the bottom of the freezing point test tube is 20 mm, obtaining a freezing point test tube with a freezing point thermometer.

[0078] (3) Place the other freezing point test tube containing the oil sample to be tested obtained in step (1) and the freezing point test tube with a freezing point thermometer obtained in step (2) into the freezing point test sleeve at the same time, and suspend the coupon into the other freezing point test tube containing the oil sample to be tested obtained in step (1). The freezing point test sleeve is directly below the tensiometer. The other end of the coupon is connected to the tensiometer by a thin line. The uppermost end of the coupon is flush with the circular scale line of the freezing point test tube, and the coupon does not touch the wall of the freezing point test tube, obtaining the device to be tested; the coupon is a 4-blade paddle coupon (denoted as coupon 3); the flat plate diameter of the double-plate coupon is 12 mm, the flat plate thickness is 0.8 mm, and the distance between the two blades is 8 mm; the diameter of the support column of the double-plate coupon is 2.8 mm and the height is 1.8 mm; the freezing point test sleeve is vertically installed in the temperature control device, the temperature control device contains coolant, the depth of the freezing point test sleeve immersed in the coolant is 100 mm, the temperature difference between the oil sample to be tested and the coolant is 15 °C, and the cooling rate of the temperature control device is 0.75 °C / min.

[0079] (4) Cool the two freezing point test tubes of the device to be tested in step (3). Use the freezing point test tube with a thermometer in step (3) as a reference sample to read the temperature. Record the reading of the tensiometer every 0.5 °C. When the reading of the tensiometer suddenly increases, record the temperature at this time, and continue to record the readings of the tensiometer three times. When the readings of the subsequent three tensiometers return to the equilibrium value before the increase, continue to record the readings of the tensiometer. When the readings of the subsequent three tensiometers are all greater than the tensile equilibrium value before the increase, the temperature recorded when the reading of the tensiometer suddenly increases is the freezing point of the oil sample to be tested.

[0080] The relationship curves of the tensile force and temperature of the tensiometer in Examples 1 to 3 are as Figure 8 shown. From Figure 8 it can be seen that the freezing points obtained using coupon 2 (i.e., Example 2) and coupon 3 (i.e., Example 3) are both 34 °C, while the freezing point obtained using coupon 1 (i.e., Example 1) is 33.5 °C. This is because at the same temperature, when the temperature is higher than the freezing point of the oil sample to be tested, the surface areas of coupon 2 and coupon 3 are larger, which helps to reduce wall slip, thereby increasing the tensile force of the oil sample shrinkage on the sample, making the increase in tensile force more obvious and the change in tensile force more significant; at the same time, the flat-shaped coupon helps to eliminate the influence of wall slip and makes the change in tensile force more obvious.

[0081] Example 4

[0082] The method is the same as that in Example 2 and is repeated three times.

[0083] Example 5

[0084] The oil sample to be tested is Changqing crude oil, and other conditions are the same as those in Example 2. Repeat three times.

[0085] Example 6

[0086] The oil sample to be tested is Linpan crude oil, and other conditions are the same as those in Example 2. Repeat three times.

[0087] Example 7

[0088] The oil sample to be tested is simulated wax oil, and other conditions are the same as those in Example 2. Repeat three times.

[0089] Comparative Example 1

[0090] Test the freezing point of the oil sample according to SY / T 0541-2009 "Determination Method for Freezing Point of Crude Oil". The oil sample to be tested is Nanyang crude oil. Repeat three times.

[0091] Comparative Example 2

[0092] Test the freezing point of the oil sample according to SY / T 0541-2009 "Determination Method for Freezing Point of Crude Oil". The oil sample to be tested is Changqing crude oil. Repeat three times.

[0093] Comparative Example 3

[0094] The pour point of the oil sample was tested according to SY / T 0541-2009 "Method for Determination of Pour Point of Crude Oil". The oil sample to be tested was Linpan crude oil, and the test was repeated three times.

[0095] Comparative Example 4

[0096] The pour point of the oil sample was tested according to SY / T 0541-2009 "Method for Determination of Pour Point of Crude Oil". The oil sample to be tested was simulated wax oil, and the test was repeated three times.

[0097] The pour points of the oil samples to be tested obtained in Examples 1 to 12 and Comparative Examples 1 to 4 are shown in Table 1:

[0098] Table 1 Pour Points of the Oil Samples to be Tested Obtained in Examples 1 to 12 and Comparative Examples 1 to 4

[0099]

[0100] As can be seen from Table 2, for various oil samples, the test results obtained by the coupon method provided by the present invention are basically consistent with those of the standard method, and the repeatability of the coupon method is significantly better than that of the standard method. In terms of operation convenience, after adding the sample by the coupon method, only the value of the tensiometer needs to be read regularly, and there is no need to repeatedly observe the pour point test tube. Therefore, it is significantly better than the traditional pour point test method. Moreover, the judgment of the gelling temperature by the coupon method depends on the reading of the tensiometer and does not require subjective visual judgment, so it is more objective. Therefore, the coupon method for testing the pour point of crude oil provided by the present invention has obvious advantages over the traditional test methods.

[0101] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for testing the freezing point of crude oil by the hanging plate method, comprising the following steps: (1) Injecting equal amounts of the oil sample to be tested into two solidification point test tubes respectively to obtain two solidification point test tubes containing the oil sample to be tested; (2) inserting a stopper with a freezing point thermometer into a freezing point test tube containing the oil sample to be tested obtained in step (1) to obtain a freezing point test tube with a freezing point thermometer; (3) placing another freezing point test tube containing the oil sample to be tested obtained in step (1) and the freezing point test tube with a freezing point thermometer obtained in step (2) into a freezing point test sleeve at the same time, and hanging a hanging piece in the other freezing point test tube containing the oil sample to be tested obtained in step (1), and connecting the other end of the hanging piece to a tensiometer to obtain a device to be tested; the hanging piece is a two-blade paddle hanging piece, a four-blade paddle hanging piece or a double-plate hanging piece; (4) Cooling the two freezing point test tubes of the device to be tested in step (3), using the freezing point test tube with the thermometer in step (3) as a reference sample for reading the temperature, recording the reading of the tensiometer every 0.5 to 1°C, when the reading of the tensiometer suddenly increases, recording the temperature at that time, and continuing to record the readings of three tensiometers, when the readings of the subsequent three tensiometers return to the equilibrium value before the increase, continue to record the readings of the tensiometer, when the readings of the subsequent three tensiometers are all greater than the tension equilibrium value before the increase, the temperature recorded when the reading of the tensiometer suddenly increases is the freezing point of the oil sample to be tested.

2. The method according to claim 1, characterized in that The freezing point test tube in step (1) is a dry and clean freezing point test tube.

3. The method according to claim 1, characterized in that In the step (1), the two freezing point test tubes and the oil sample to be tested are preheated before injecting equal amounts of the oil sample to be tested into the two freezing point test tubes.

4. The method according to claim 3, characterized in that The preheating temperature is 35-70° C., and the preheating time is 20-40 minutes.

5. The method according to claim 1, characterized in that In the step (1), the injection amount of the oil sample to be tested is to the annular mark of 50±3 mm on the solidification point test tube.

6. The method according to claim 1, characterized in that In the step (2), the freezing point thermometer in the freezing point test tube is perpendicular to the center of the freezing point test tube; the distance between the mercury ball of the freezing point thermometer and the bottom of the freezing point test tube is 20±2 mm.

7. The method according to claim 1, characterized in that In the step (3), the solidification point test sleeve is directly below the tensile gauge.

8. The method according to claim 1, characterized in that In the step (3), the width of the 2-blade paddle hanger is 10-13 mm, the height of the paddle blades of the 2-blade paddle hanger is 10-13 mm, and the thickness of the paddle blades of the 2-blade paddle hanger is 0.5-1 mm; the width of the 4-blade paddle hanger is 10-13 mm, the height of the paddle blades of the 4-blade paddle hanger is 10-13 mm, and the thickness of the paddle blades of the 4-blade paddle hanger is 0.5-1 mm; the diameter of the plate of the double-plate hanger is 10-13 mm, the thickness of the plate of the double-plate hanger is 0.5-1 mm, and the distance between the two paddle blades of the double-plate hanger is 6-10 mm; the diameter of the support columns of the 2-blade paddle hanger, the 4-blade paddle hanger and the double-plate hanger are independently 2.5-3 mm, and the height is independently 1.5-2 mm.

9. The method according to claim 1, characterized in that: In the step (3), the hanging piece is connected to the tensile gauge via a thin wire, the uppermost end of the hanging piece is flush with the annular marking line of the freezing point test tube, and the hanging piece does not touch the wall surface of the freezing point test tube.

10. The method according to claim 1, characterized in that In the step (3), the solidification point test sleeve is vertically installed in a temperature control device, and the temperature control device contains a coolant; the depth of the solidification point test sleeve immersed in the coolant is ≥100mm; the temperature difference between the temperature of the oil sample to be tested and the coolant is 10 to 25°C; the cooling rate of the temperature control device is 0.5 to 1°C / min.

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